1. Field of the Invention
The present invention relates to a solid electrolytic capacitor of the superposed foil type having a good performance.
2. Description of the Related Art
A metal having a valve action (hereinafter referred to as "valve metal"), such as tantalum, aluminum, niobium or titanium, is used as a positive electrode substrate of the conventional solid electrolytic capacitor. Of these, tantalum and aluminum are often adopted.
For example, a solid electrolytic capacitor comprising aluminum as the positive electrode substrate has a section as shown in FIG. 1. Referring to FIG. 1, an aluminum oxide film which is a dielectric substance is formed on the surface of a sintered body of aluminum powder to form a positive electrode substrate 2. A semiconductor layer 3 is formed on this aluminum oxide film and electroconductive layers 4 and 5 are foamed on the semiconductor layer 3 to form a solid electrolytic capacitor. Manganese dioxide formed by thermal decomposition is mainly used as the semiconductor layer 3. Note, reference numerals 1 and 6 represent a positive electrode terminal and a solder layer, respectively.
However, the conventional solid electrolytic capacitor has problems in that, since thermal decomposition is carried out several times in the preparation process, the preparation steps become complicated, and the equivalent series resistance in the high-frequency band region is too large.